Dewalt dc 5 500'motor runs ok on battery well as on mains but has no suction filter seems to be ok

Are you sure the main vacuum motor is running ? There are 2 motors. A vacuum motor and a brushroll motor. If the brush is turning but the vac motor isn't running it would not pick up anything. Could be a bad switch or a bad vac motor. Take it to your local vac shop for assessment.

there are replaceable parts in motor, it must be replaced.
DeWALT DC728 Parts List and Diagram Type 1 eReplacementParts com

On what unit? An extractor?

if there's no blockages and filters all OK it's probably the suction fan that as worn down and not creating as much suction..

ive had the dyson apart and cant find a blockage, the motor sounds ok.

Hi,

Did you dry the filter for 12 hours before reinstalling and giving a go? Most suction problems are from a blockage of some kind. The Dyson website seems to think it's the filter.
Here is a website which has instructions on washing the filter: http://www.dyson.com/support/help.asp?article=1464&product=DC07-SY-HEPA_US

Hope this works for you. If it does, I'd appreciate your vote. Thanks,

Handie Andie

Assuming the unit (motor) runs ok and since it used, you may need to disassemble it and check the suction right at the motor. Sometimes there is a filter screen in front of it that can plug. The motor impeller could be partially obstructed or dirty, reducing the vacuum force. The bag should be the correct one for the unit or suction can be lost if it doesn't fit correctly.

Is there suction where the pipe hooks to the cannister? If so, then are all of the outlets without suction? Maybe the hose is plugged. If the hose is ok, and there is suction at the cannister, then **** up a small **** of paper, one for each room outlet, have a number on each piece of paper, Which ever one doesn't ,ake it thru to the cannasiter is the outlet that is plugged. You can use a plumbers snake to clean out a clogged outlet or even a clogged hose.

If the motors are running and sound ok, then there has to be suction at the outlet on the cannister. If the filter bag is old, it may be best to replace it with a new one.

You should check the disc filter that is located under the paper cone support. The support is secured with a single screw in the middle at the bottom. This filter is commonly overlooked and when it gets dirty will restrict airflow and cause the motor to overheat. Most motors have a Hi-Limit switch incorporated into the motor to protect against overheating. You should also check the top filter (which is probably foam) and replace if it is clogged.

the problem on your vacuum is the dc - dc converter.u cna replace them but to follow the same connection.